Limitations of using smoke exhaust rate determined based on empirical fire plume model to achieve perpetual tenability

In many jurisdictions around the world, such as Singapore, fire authorities could impose a more stringent requirement of perpetual tenability for some key fire protection sites of national and cultural importance such as airports, large-scale indoor gardens, national Art Galleries/Museums, etc. than the usual acceptance criteria of Available Saft Egress Time (ASET) / Required Safe Egress Time (RSET) ≥ 2 in performance-based designs. In designing the Engineered Smoke Control (ESC) system, fire engineering designers often face the challenge that using a smoke exhaust rate determined based on the empirical fire plume model (a method widely used in prescriptive fire codes and an often-used reference to design the smoke exhaust rate in performance-based designs) cannot achieve perpetual tenability. For buildings with fire safety systems designed following the prescriptive codes, there is no need to conduct performance validation (be it simulation or experiment) on those designs before being accepted by fire authorities since the prescriptive code is often considered very conservative with ample safety margin and redundancy. This paper investigates the question of why using the same engineering principle of stabilising the smoke layer depth at a design height based on the empirical fire plume model would fail to achieve perpetual tenability.